Summary The Beechcraft King Air200 (registration C-FCGL, serial numberBB190), with two pilots and two paramedics on board, departed Prince George Airport, British Columbia, at 1228 Pacific standard time on an instrument flight rules medical evacuation flight to Cranbrook, British Columbia. The flight was dispatched to transport two patients from Cranbrook to Kelowna. During cruise flight at 15000feet above sea level, the aircraft was in icing conditions. The aircraft's ice-protection equipment dealt effectively with the icing conditions until about 45minutes after take-off, when the aircraft began to accumulate ice at a rate that exceeded the capabilities of the ice-protection equipment. The airspeed decreased to the point that a descent was required, and, despite the crew selecting maximum available engine power, the aircraft descended from 15000 to 10800feet, below the minimum obstacle clearance altitude for the area. Vancouver air traffic control issued emergency vectors to guide the aircraft down the Arrow Lakes area to avoid high terrain. Several minutes later, the pilots advised that they were clear of cloud and proceeding to Kelowna. Accumulated ice, up to six inches thick, was shed during the approach to Kelowna, where an uneventful landing was made. Ce rapport est galement disponible en franais. Other Factual Information About 20minutes1 prior to departure from Prince George, the pilot-in-command (PIC) reviewed TAFs, METARs and SIGMETs2 via an Internet weather information site. None of the information that was reviewed indicated icing conditions, forecast or actual, along the intended route. Based on this information, the PIC determined that the weather conditions were suitable for an instrument flight rules flight at 15000feet from Prince George to Cranbrook to Kelowna. The graphical area forecast, which the PIC did not review, called for mixed moderate icing between the freezing level and 16000feet for about two-thirds of the planned flight route. The Transport Canada-approved flight manual for the Beechcraft King Air200 states, in part, that although the aircraft is approved for flight in icing conditions as described in the U.S. Code of Federal Regulations (CFR),3 it is not approved for flight in severe icing conditions or other conditions that exceed the capabilities of the aircraft ice-protection equipment. Flight into icing conditions which lie outside the CFR-defined conditions is not prohibited; however, pilots must be prepared to divert the flight promptly if hazardous ice accumulations occur. In cruising flight, the aircraft's true airspeed was 230knots, providing an estimated time en route of 1hour 30minutes. For about 40minutes after departing Prince George, the icing conditions encountered were light to moderate and the aircraft's ice-protection equipment prevented excessive ice accumulation. However, the accumulation of ice began to exceed the capabilities of the ice-protection equipment and the aircraft's speed started to decrease. The pilots began planning descent and diversion but determined that there were no suitable airports within range. The ice accumulation increased and, when the airspeed decreased to 150knots, the crew had to start descending. The pilots requested a descent to the lowest possible safe altitude for the area, and the controller issued a descent to 13900feet, the 100nautical mile safe altitude for Cranbrook Airport. The descent was continued, but on reaching the assigned altitude, the descent could not be arrested, although the power levers were advanced until the engines were operating at their redline inter-turbine temperature (ITT). The airspeed decreased to 140knots, the descent rate was 1500-2000feet per minute, and there was significant airframe and control surface buffeting. As the aircraft descended, in a power-on stall condition, through 12000feet, the pilots notified air traffic control (ATC) that they were unable to maintain altitude and further descent was required. The pilot then advanced the engine power levers to the forward stops, causing both engines to continuously exceed the maximum ITT and torque limits. ATC instructed the King Air to turn left 90to bring the aircraft over Upper Arrow Lake and clear of high terrain. Although the King Air stopped accumulating ice as it descended through 11000feet, the ice already accumulated prevented the aircraft from levelling off. Radar data indicate that the aircraft descended as low as 10800feet. Shortly after, the controller advised the pilots that they were likely over Arrow Lake and 10000feet was a safe altitude for their location. An overflying de Havilland DHC-8 informed ATC that the weather appeared better to the west of Arrow Lake. The controller vectored the King Air southwest toward Kelowna. Shortly thereafter, the King Air entered visual meteorological conditions and the pilot was able to retard the engine power levers to bring all engine operating parameters within the approved limits. During the period the King Air was in severe icing conditions, the aircraft nose attitude was maintained 5and 10up and the pilots experienced significant airframe and flight control buffeting, with the rudder pedals buffeted almost half-deflection. Although the portion of the leading edge of the horizontal stabilizer that the flight crew could see appeared to be shedding ice, the aircraft was in a full power-on stall during much of the descent to 11000feet. When the controller instructed the King Air to turn left to follow the lake, the pilots had great difficulty in banking the aircraft more than5. Subsequent to the incident, both engines were removed from service because they had been operated above their temperature and torque limits for about seven minutes.